tannin

tannin   tannic acid, or gallotannic acid, astringent vegetable product found in a wide variety of plants. Sources include the bark of oak, hemlock, chestnut, and mangrove; the leaves of certain sumacs; and plant galls. Tannin is also present in tea, coffee, and walnuts. A solution of tannic acid is obtained from one of these natural sources by extraction with hot water; in particular, gallotannic acid is obtained from plant gall. Tannin varies somewhat in composition, having the approximate empirical formula C ₇₆ H ₅₂ O ₄₆ . Tannic acid is a colorless to pale yellow solid; it is believed to be a glucoside in which each of the five hydroxyl groups of the glucose molecule is esterified with a molecule of digallic acid. Tannin is used in tanning animal skins to make leather; it transforms certain proteins of animal tissue into compounds that resist decomposition. It is also used in manufacturing inks, as a mordant in dyeing, and in medicine as an astringent and for treatment of burns.

tannin One of a group of complex organic chemicals commonly found in leaves, unripe fruits, and the bark of trees. Their function is uncertain: the unpleasant taste may discourage grazing animals, or they may help form barriers against the entry of pathogens. Some tannins have commercial uses, notably in the production of leather and ink.

tannin (tannic acid) Any of a group of complex organic compounds derived from tree bark, roots and galls, unripe fruit, tea and coffee. Tannin is used in tanning to cure hides and make leather, in inks and dyes, and as an astringent in medicine.